Denise Roche

Faster pulmonary oxygen uptake kinetics in trained versus untrained male adolescents.

UNLABELLED Exercise training results in a speeding of pulmonary oxygen uptake (VO2) kinetics at the onset of exercise in adults; however, only limited research has been conducted with children and adolescents. PURPOSE The aim of the present study was to examine VO2 and muscle deoxygenation kinetics in trained and untrained male adolescents. METHODS Sixteen trained (15 +/- 0.8 yr, VO2peak = 54.7 +/- 6.2 mL x kg-1 x min-1, self-assessed Tanner stage range 2-4) and nine untrained (15 +/- 0.6 yr, VO2peak = 43.1 +/- 5.2 mL x kg-1 x min-1, Tanner stage range 2-4) male adolescents performed two 6-min exercise transitions from a 3-min baseline of 10 W to a workload equivalent to 80% lactate threshold separated by a minimum of 1 h of passive rest. Oxygen uptake (breath-by-breath) and muscle deoxygenation (deoxyhemoglobin signal from near-infrared spectroscopy) were measured continuously throughout baseline and exercise transition. RESULTS The time constant of the fundamental phase of VO2 kinetics was significantly faster in trained versus untrained subjects (trained: 22.3 +/- 7.2 s vs untrained: 29.8 +/- 8.4 s, P = 0.03). In contrast, neither the time constant (trained: 9.7 +/- 2.9 s vs untrained: 10.1 +/- 3.4 s, P = 0.78) nor the mean response time (trained: 17.4 +/- 2.5 s vs untrained: 18.3 +/- 2.3 s, P = 0.39) of muscle deoxygenation kinetics differed with training status. CONCLUSIONS The present data suggest that exercise training results in faster VO2 kinetics in male adolescents, although inherent capabilities cannot be ruled out. Because muscle deoxygenation kinetics were unchanged, it is likely that faster VO2 kinetics were due to adaptations to both the cardiovascular system and the peripheral musculature.

Physical activity and psychological well-being in children with Type 1 diabetes

Abstract Physical activity and psychological well-being contribute to positive lifestyle and well-being in youngsters who have Type 1 diabetes. The aims of this study were to objectively assess the physical activity levels of children with Type 1 diabetes, and investigate associations between physical activity levels, psychological well-being and HbA1c. Thirty-six children, mean age 12.8 years, participated in the investigation. Physical activity was assessed using heart rate monitoring over four days. Children further completed the Diabetes Quality of Life for Youths Questionnaire, the Physical Self-Perception Profile for Children and the Self-Efficacy for Diabetes Scale. Routine outpatient HbA1c measurements were recorded. There were no significant associations between psychological well-being and physical activity, or HbA1c and physical activity, thus suggesting physical activity does not directly relate to psychological well-being in children with Type 1 diabetes. It may be that the effect of physical activity differs from that in children without Type 1 diabetes because of the place of physical activity within diabetes management and the need to balance this with insulin dosage and dietary intake to maintain blood glucose levels.

Time-of-Day Effect on Cardiac Responses to Progressive Exercise

This study was designed to examine time-of-day effects on markers of cardiac functional capacity during a standard progressive cycle exercise test. Fourteen healthy, untrained young males (mean ± SD: 17.9 ± 0.7 yrs of age) performed identical maximal cycle tests in the morning (08:00–11:00 h) and late afternoon (16:00–19:00 h) in random order. Cardiac variables were measured at rest, submaximal exercise, and maximal exercise by standard echocardiographic techniques. No differences in morning and afternoon testing values at rest or during exercise were observed for oxygen uptake, heart rate, cardiac output, or markers of systolic and diastolic myocardial function. Values at peak exercise for Vo2 at morning and afternoon testing were 3.20 ± 0.49 and 3.24 ± 0.55 L min−1, respectively, for heart rate 190 ± 11 and 188 ± 15 bpm, and for cardiac output 19.5 ± 2.8 and 19.8 ± 3.5 L min−1. Coefficients of variation for morning and afternoon values for these variables were similar to those previously published for test-retest reproducibility. This study failed to demonstrate evidence for significant time-of-day variation in Vo2max or cardiac function during standard progressive exercise testing in adolescent males. (Author correspondence: thomas.rowland@bhs.org)

Sex influence on myocardial function with exercise in adolescents

Ventricular systolic functional response to exercise has been reported to be superior in adult men compared to women. This study explored myocardial responses to maximal upright progressive exercise in late pubertal males and females.

Prior exercise speeds pulmonary oxygen uptake kinetics and increases critical power during supine but not upright cycling

What is the central question of this study? Critical power (CP) represents the highest work rate for which a metabolic steady state is attainable. The physiological determinants of CP are unclear, but research suggests that CP might be related to the time constant of phase II oxygen uptake kinetics ( τV̇O2 ). What is the main finding and its importance? We provide the first evidence that τV̇O2 is mechanistically related to CP. A reduction of τV̇O2 in the supine position was observed alongside a concomitant increase in CP. This effect may be contingent on measures of oxygen availability derived from near‐infrared spectroscopy.

RER variability analysis by sample entropy: comparing trained and untrained adolescent female soccer players

Economy of movement is defmed as the mass related aerobic demand (V02 mL·kg-l·min-l) or energy expenditure required to run or walk at a given submaximal speed (Morgan, 2000). It has been well established that children have a lower economy compared to adults (Rowland and Green, 1988; Rowland et al., 1987; Unnithan and Eston, 1990). This means that at any given walking or running speed, children exhibit a higher weight relative V02compared to that of an adult. The difference in economy between children and adults is thought to be due to differences in stride frequency (SF), leg length, body-surface-area to mass ratio (BSA:M), body mass index (BMI), and ventilatory efficiency (Rowland et al., 1987; Rowland and Green, 1988; Unnithan and Eston, 1990).

Elevated baseline work rate slows pulmonary oxygen uptake kinetics and decreases critical power during upright cycle exercise

Critical power is a fundamental parameter defining high‐intensity exercise tolerance, and is related to the phase II time constant of pulmonary oxygen uptake kinetics ( τV˙O2 ). Whether this relationship is causative is presently unclear. This study determined the impact of raised baseline work rate, which increases τV˙O2 , on critical power during upright cycle exercise. Critical power was determined via four constant‐power exercise tests to exhaustion in two conditions: (1) with exercise initiated from an unloaded cycling baseline (U→S), and (2) with exercise initiated from a baseline work rate of 90% of the gas exchange threshold (M→S). During these exercise transitions, τV˙O2 and the time constant of muscle deoxyhemoglobin kinetics (τ[HHb + Mb]) (the latter via near‐infrared spectroscopy) were determined. In M→S, critical power was lower (M→S = 203 ± 44 W vs. U→S = 213 ± 45 W, P = 0.011) and τV˙O2 was greater (M→S = 51 ± 14 sec vs. U→S = 34 ± 16 sec, P = 0.002) when compared with U→S. Additionally, τ[HHb + Mb] was greater in M→S compared with U→S (M→S = 28 ± 7 sec vs. U→S = 14 ± 7 sec, P = 0.007). The increase in τV˙O2 and concomitant reduction in critical power in M→S compared with U→S suggests a causal relationship between these two parameters. However, that τ[HHb + Mb] was greater in M→S exculpates reduced oxygen availability as being a confounding factor. These data therefore provide the first experimental evidence that τV˙O2 is an independent determinant of critical power. Keywords critical power, exercise tolerance, oxygen uptake kinetics, power‐duration relationship, muscle deoxyhemoglobin kinetics, work‐to‐work exercise.